Atrios

Atrios is the third planet in the trinity of related planets in the Dundra System, with the other two being Darios and Atrios-6. It formed from the same rock as Darios and indirectly from Atrios-6, during a sizeable asteroid collision with a large planet in the solar system.

Atrios is only ever mentioned in passing by Matt or Aurora, but never visited. It is heavily implied that Atrios is very similar in composition to the other two planets, given their similarity in formation and same age. Atrios and Atrios-6 are likely named similarly for this reason.